1. Field of the Invention
This invention relates to an electronic endoscope and an endoscopic system which are used for various purposes such as industrial or medical purposes.
2. Description of the Related Art
In general, an observation optical system is arranged in an insertion portion of an electronic endoscope and, in particular, an objective lens and a solid-state image sensing device (a CCD) connected with an imaging cable extended toward a proximal end side of the inserting portion are arranged in a distal end portion of the insertion portion. In practice, the objective lens is held in an objective lens frame, the solid-state image sensing device is held in a CCD holding frame, and these members are arranged in the distal end portion of the insertion portion of the endoscope with the CCD holding frame being assembled to a rear end of the objective lens frame. In regard to the endoscope, an image formed on the solid-state image sensing device through the objective lens is acquired by the solid-state image sensing device, the image is converted into an electrical signal, and the electrical signal is output to a video processor which is provided outside the endoscope through the imaging cable, thereby displaying a video picture in a monitor.
In recent years, for example, a high-frequency treatment device is combined with an electronic endoscope and used in some cases. In such a situation, a leak current from the high-frequency treatment device may flow through a solid-state image sensing device from a distal end portion of an insertion portion of the endoscope, and an observation image obtained by the endoscope may be affected by noise. Furthermore, when static electricity is produced during use of the endoscope, a current obtained by the static electricity may flow through the solid-state image sensing device from the distal end portion of the endoscope.
For example, a distal end portion main body of an insertion portion of an endoscope disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-128936 is generally formed of a conductive metal member, and the distal end main body is contact with a metal structure member constituting an exterior and an inner structure of the endoscope. For example, static electricity or a leak current from a high-frequency treatment device is electrically connected to the metal structure member by allowing the current to flow through the metal structure member of the endoscope via the distal end portion main body. When the current is let to flow through a ground portion of a video processor outside the endoscope, the current is prevented from flowing through a solid-state image sensing device.
Further, in recent years, there is an endoscope in which a distal end portion main body of an insertion portion is made of a transparent insulating material (a non-conductive material). This configuration is adopted because of a reduction in price cost attained by integrating an illumination lens provided to the distal end portion main body with the distal end portion main body or a reduction in diameter of the distal end portion main body. In case of the endoscope, since the distal end portion main body is made of the non-conductive material, the distal end portion main body of the insertion portion of the endoscope cannot be electrically connected to the metal structure member as different from Jpn. Pat. Appln. KOKAI Publication No. 2001-128936. Therefore, static electricity or a high-frequency leak current flows through a metal objective lens frame exposed from the distal end portion main body, and the current may possibly flow through the solid-state image sensing device via a CCD holding frame.
To solve such problems, Jpn. Pat. Appln. KOKAI Publication No. 2007-89888 discloses a technology for electrically connecting a CCD reinforced frame, to which a rear end of a CCD holding frame is fitted and which covers an imaging substrate to assure strength of a solid-state image sensing device or the imaging substrate, with a GND of an imaging cable by using a conducive wire arranged in an insertion portion. Based on the countermeasure, a current that has flowed in an objective lens frame to flow through the CCD holding frame does not flow through the solid-state image sensing device but flows to the GND of a video processor via the CCD reinforcing frame, the conductive wire, and the GND of the imaging cable. Therefore, in the endoscope disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-89888, an influence of static electricity or a high-frequency leak current on the solid-state image sensing device is avoided. In the endoscope disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-89888, to enhance conductive properties between the objective lens frame, the CCD holding frame, and the CCD reinforce frame, the objective lens frame is bonded to the CCD holding frame and the CCD holding frame is bonded to the CCD reinforced frame by using a conductive adhesive.